1. Field of the Invention
The present invention relates to a cooling system suitably adapted for cooling a sample mounted on a measuring apparatus such as an X-ray diffractometer.
2. Prior Art
In measuring a sample using a measuring apparatus such as an X-ray diffractometer, the sample serving as a measuring object is first rendered cryogenic, and then it is diffracted in its crystal structure, etc. in such a state. In such a measurement, a cooling system is employed for rendering the sample cryogenic.
As a prior cooling system of this type, there is known an arrangement in which liquid nitrogen is first stored in a storage tank, then it is rendered gaseous by a suitable amount, and thereafter it is supplied to a nozzle pipe so that low-temperature nitrogen gas is jetted toward the sample through the tip end of the nozzle pipe.
FIG. 4 is a view showing an arrangement of the prior art cooling system of this type. As shown in the same figure, liquid nitrogen is first sealed and stored in a storage tank 100, and then it is heated by a heater 101 so that it is rendered gaseous by a suitable amount and is changed to nitrogen gas. The nitrogen gas thus generated is supplied to a nozzle body 103 through a pipe 102 coupled to the nozzle body 103. In the nozzle body 103, the temperature of the nitrogen gas is changed to a proper value by a temperature control heater 105 while it is controlled by a thermo couple 104, then the nitrogen gas is jetted from a tip end opening of a nozzle pipe 106 coupled to the nozzle body 103.
The liquid nitrogen is changed to dry gas when moisture thereof is removed by a drying heater 107 coupled to the storage tank 100, and the thus changed dry gas is supplied to an outer periphery of the nozzle pipe 106 through a pipe 108 coupled to the drying heater 107. As a result, it is possible to prevent frost from adhering to the tip end of the nozzle pipe 106 when the dry gas is supplied or jetted from the pipe 108 to the tip end of the nozzle pipe 106.
As mentioned above, the prior art cooling system of this type uses liquid nitrogen as a cooling medium. The liquid nitrogen is generally expensive. Further, careful attention must be paid when the liquid nitrogen is carried or handled, and it is sometimes difficult to be carried depending on the location where it is used, whereby the measurement of the sample is sometimes difficult to perform.
For example, it is not unusual that a X-ray diffraction measurement lasts for a long period of time of more than one week. There occurs such problems in that first the amount of liquid nitrogen used during the period sometimes exceeds, e.g. 100 liter, secondly it takes time and labor to carry and supply the liquid nitrogen, and thirdly it is expensive.
On the other hand, there are following problems for the structure of the nozzle pipe 106.
FIG. 5 is an enlarged cross sectional front view showing the tip end of the nozzle pipe used for a prior art cooling system.
As shown in FIG. 5, the nozzle pipe 106 of this type is a triple-structured pipe comprising an inner pipe 201, an outer pipe 202 and a vacuum adiabatic pipe 203, which is coaxially arranged between the inner pipe 201 and the outer pipe 202.
That is, the vacuum adiabatic pipe 203 is provided coaxially around the outer periphery of the inner pipe 201 with a given interval, and the outer pipe 202 is also provided coaxially around the outer periphery of the vacuum adiabatic pipe 203 with a given interval. The tip end 203a of the vacuum adiabatic pipe 203 is closed at a position a little behind the tip end of the inner pipe 201. An adiabatic space 204 is formed between the vacuum adiabatic pipe 203 and the inner pipe 201. Air in the adiabatic space 204 is attracted by a vacuum pump, not shown, to thereby render the inner pipe 201 adiabatic.
Nitrogen gas serving as a cooling medium is passed through the inner pipe 201 and is jetted from the tip end opening thereof. There is a method of blowing dry gas toward the tip end of the nozzle pipe 106 through a tip end of a pipe 108 which is provided separately from the nozzle pipe 106 (refer to FIG. 4) to prevent frost from adhering to the tip end of the nozzle pipe 106. However, there are the following drawbacks in this method. That is, an operation to install or connect the nozzle pipe 106 and the pipe 108 to a measuring apparatus is troublesome, and a jetting direction of the nitrogen gas is liable to be changed when the dry gas is blown out from different directions.
Accordingly, the nozzle pipe 106 has a structure as shown in FIG. 5 in which dry gas is supplied to a space defined between the outer pipe 202 and the vacuum adiabatic pipe 203 and it is jetted from the tip end opening of the outer pipe 202, thereby preventing frost from adhering to the tip end of the inner pipe 201.
Use of this nozzle in the arrangement of FIG. 4 can dispense with the pipe 108, thereby facilitating the installation of the nozzle pipe 106 and preventing the jetting direction of the nitrogen gas from being changed by the dry gas.
However, when analyzing the structure of the tip end of the nozzle pipe 106, the tip end (closed end) 203a of the vacuum adiabatic pipe 203 has a stepped shape, and a tip end portion 201a of the inner pipe 201 is slightly extended from the vacuum adiabatic pipe 203.
Accordingly, there occurs frequently such a problem that the turbulence of dry air current is generated in a space extending from the tip end 203a (stepped shape) of the vacuum adiabatic pipe 203 to the tip end opening of the outer pipe 202 so that fresh air including humidity turns around and directs toward the tip end of the inner pipe 201.
When the fresh air including humidity adheres to the tip end of the inner pipe 201, even if the amount of moisture adhered thereto is very slight, there is a possibility that the humidity or moisture adhered to the tip end of the inner pipe 201 is changed to frost and the frost grows to thereby lower cooling performance, especially when a measurement takes a long period of time (there is a possibility of a continuous measurement lasting for more than one week for analyzing a single-crystal sample using an X-ray diffractometer).